Recent Advances on Conducting Polymers Based Nanogenerators for Energy Harvesting

A Review of Polymer-Based Environment-Induced Nanogenerators: Power Generation Performance and Polymer Material Manipulations

Natural environment hosts a considerable amount of accessible energy, comprising mechanical, thermal, and chemical potentials. Environment-induced nanogenerators are nanomaterial-based electronic chips that capture environmental energy and convert it into electricity in an environmentally friendly way. Polymers, characterized by their superior flexibility, lightweight, and ease of processing, are considered viable materials. In this paper, a thorough review and comparison of various polymer-based nanogenerators were provided, focusing on their power generation principles, key materials, power density and stability, and performance modulation methods. The latest developed nanogenerators mainly include triboelectric nanogenerators (TriboENG), piezoelectric nanogenerators (PENG), thermoelectric nanogenerators (ThermoENG), osmotic power nanogenerator (OPNG), and moist-electric generators (MENG). Potential practical applications of polymer-based nanogenerator were also summarized. The review found that polymer nanogenerators can harness a variety of energy sources, with the basic power generation mechanism centered on displacement/conduction currents induced by dipole/ion polarization, due to the non-uniform distribution of physical fields within the polymers. The performance enhancement should mainly start from strengthening the ion mobility and positive/negative ion separation in polymer materials. The development of ionic hydrogel and hydrogel matrix composites is promising for future nanogenerators and can also enable multi-energy collaborative power generation. In addition, enhancing the uneven distribution of temperature, concentration, and pressure induced by surrounding environment within polymer materials can also effectively improve output performance. Finally, the challenges faced by polymer-based nanogenerators and directions for future development were prospected.

An Emerging Era: Conformable Ultrasound Electronics

Conformable electronics are regarded as the next generation of personal healthcare monitoring and remote diagnosis devices. In recent years, piezoelectric-based conformable ultrasound electronics (cUSE) have been intensively studied due to their unique capabilities, including nonradiative monitoring, soft tissue imaging, deep signal decoding, wireless power transfer, portability, and compatibility. This review provides a comprehensive understanding of cUSE for use in biomedical and healthcare monitoring systems and a summary of their recent advancements. Following an introduction to the fundamentals of piezoelectrics and ultrasound transducers, the critical parameters for transducer design are discussed. Next, five types of cUSE with their advantages and limitations are highlighted, and the fabrication of cUSE using advanced technologies is discussed. In addition, the working function, acoustic performance, and accomplishments in various applications are thoroughly summarized. It is noted that application considerations must be given to the tradeoffs between material selection, manufacturing processes, acoustic performance, mechanical integrity, and the entire integrated system. Finally, current challenges and directions for the development of cUSE are highlighted, and research flow is provided as the roadmap for future research. In conclusion, these advances in the fields of piezoelectric materials, ultrasound transducers, and conformable electronics spark an emerging era of biomedicine and personal healthcare.

Materials Nanoarchitectonics at Dynamic Interfaces: Structure Formation and Functional Manipulation

The next step in nanotechnology is to establish a methodology to assemble new functional materials based on the knowledge of nanotechnology. This task is undertaken by nanoarchitectonics. In nanoarchitectonics, we architect functional material systems from nanounits such as atoms, molecules, and nanomaterials. In terms of the hierarchy of the structure and the harmonization of the function, the material created by nanoarchitectonics has similar characteristics to the organization of the functional structure in biosystems. Looking at actual biofunctional systems, dynamic properties and interfacial environments are key. In other words, nanoarchitectonics at dynamic interfaces is important for the production of bio-like highly functional materials systems. In this review paper, nanoarchitectonics at dynamic interfaces will be discussed, looking at recent typical examples. In particular, the basic topics of "molecular manipulation, arrangement, and assembly" and "material production" will be discussed in the first two sections. Then, in the following section, "fullerene assembly: from zero-dimensional unit to advanced materials", we will discuss how various functional structures can be created from the very basic nanounit, the fullerene. The above examples demonstrate the versatile possibilities of architectonics at dynamic interfaces. In the last section, these tendencies will be summarized, and future directions will be discussed.

Influence of the Foaming Process on the Burning Behavior of the PET-PEN Copolymer

The manufacturing process can modify the micromechanical structure, usefulness, and functionality of foams. Although one-step foaming is a simple process, controlling the morphology of the foams is difficult compared to the two-step processing method. In this study, we investigated the experimental differences in thermal and mechanical properties, particularly combustion behavior, between PET-PEN copolymers prepared by the two methods. With an increase in foaming temperature T_f, the PET-PEN copolymers became more fragile, and the breaking stress of the one-step PET-PEN foamed at the highest T_f was only 2.4% of that of the raw material. For the pristine PET-PEN, 24% of the mass was burned, leaving 76% as a molten sphere residue. The two-step MEG PET-PEN had only 1% of its mass remaining as a residue, whereas the one-step PET-PENs had between 41 and 55%. The actual mass burning rates were similar for all the samples except the raw material. The coefficient of thermal expansion of the one-step PET-PEN was about two orders of magnitude lower than that of the two-step SEG.

Recent Progress on Hydrogel-Based Piezoelectric Devices for Biomedical Applications

Flexible electronics have great potential in the application of wearable and implantable devices. Through suitable chemical alteration, hydrogels, which are three-dimensional polymeric networks, demonstrate amazing stretchability and flexibility. Hydrogel-based electronics have been widely used in wearable sensing devices because of their biomimetic structure, biocompatibility, and stimuli-responsive electrical properties. Recently, hydrogel-based piezoelectric devices have attracted intensive attention because of the combination of their unique piezoelectric performance and conductive hydrogel configuration. This mini review is to give a summary of this exciting topic with a new insight into the design and strategy of hydrogel-based piezoelectric devices. We first briefly review the representative synthesis methods and strategies of hydrogels. Subsequently, this review provides several promising biomedical applications, such as bio-signal sensing, energy harvesting, wound healing, and ultrasonic stimulation. In the end, we also provide a personal perspective on the future strategies and address the remaining challenges on hydrogel-based piezoelectric electronics.

Molecular Machines and Microrobots: Nanoarchitectonics Developments and On-Water Performances

This review will focus on micromachines and microrobots, which are objects at the micro-level with similar machine functions, as well as nano-level objects such as molecular machines and nanomachines. The paper will initially review recent examples of molecular machines and microrobots that are not limited to interfaces, noting the diversity of their functions. Next, examples of molecular machines and micromachines/micro-robots functioning at the air-water interface will be discussed. The behaviors of molecular machines are influenced significantly by the specific characteristics of the air-water interface. By placing molecular machines at the air-water interface, the scientific horizon and depth of molecular machine research will increase dramatically. On the other hand, for microrobotics, more practical and advanced systems have been reported, such as the development of microrobots and microswimmers for environmental remediations and biomedical applications. The research currently being conducted on the surface of water may provide significant basic knowledge for future practical uses of molecular machines and microrobots.